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Phytophthora ramorum. Part 3 - Regulations and Management of Phytophthora ramorum. A short course Presented by the California Oak Mortality Task Force. Background Photo Credits: Karl Buermeyer, UC Cooperative Extension (forest scenes, lone oak)

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phytophthora ramorum

Phytophthora ramorum

Part 3 - Regulations and Management of Phytophthora ramorum

A short course

Presented by the

California Oak Mortality Task Force

Background Photo Credits:

Karl Buermeyer, UC Cooperative Extension (forest scenes, lone oak)

Stephen Eales, Plant Health and Seed Inspectorate, DEFRA, UK (mountain laurel)

Jan Hedberg, Oregon Department of Agriculture (viburnums in nursery)

Steve Tjosvold, UC Cooperative Extension (rhododendron)

course outline

Part 1 - Introduction to Phytophthora ramorum and Sudden Oak Death

Course Outline

Part 2 -Symptom Recognition, Diagnosis, and Sampling

  • Part 3 - Regulations and Management of Phytophthora ramorum
    • Regulations and Quarantines
    • Minimizing Spread in Wildlands and Landscapes
    • Preventing Disease Transfer between Nurseries
    • Preventing Infection from Surrounding Woodlands
    • Preventing Favorable Disease Conditions in the Nursery
    • Preventative Chemical Treatments
    • Review Questions

Part 3Regulations and Management of Phytophthora ramorum

Regulations and quarantines have been established to minimize the artificial spread of Phytophthora ramorum. Best Management Practices (BMPs) have been developed to aid in disease prevention.


Regulations and Quarantines

In California, County Agricultural Commissioners and the California Department of Food and Agriculture are responsible for enforcing quarantines, and for dealing with nursery detections as well as wildland infestations. The California Department of Forestry and Fire Protection enforces regulations to prevent disease spread during timber operations on private land in infested areas. The USDA Animal and Plant Health Inspection Service (APHIS) regulates interstate commerce, and works with other countries to develop international shipping agreements.

As of April 2004, countries with regulations on the importation of Phytophthora ramorum host material include: Canada, the UK, South Korea, New Zealand, Australia, the Czech Republic, Mexico, Taiwan, the US, the European Union, and others.


Since regulations and quarantines vary from region to region and are subject to change, it is best to refer to the following resources for up-to-date regulatory information:

  • California Department of Food and Agriculture:
  • California County Agricultural Commissioners:
  • Oregon Department of Agriculture:
  • Washington State Department of Agriculture:
  • Canadian Food Inspection Agency: 01e.shtml
  • Department for Environment, Food and Rural Affairs (UK)
  • Users in states other than California, Washington, and Oregon should contact their state or county agriculture departments.

Minimizing Spread in Wildlands and Landscapes

As described in Part 1 of this course, under “Biology,” Phytophthora ramorum survives and spreads best under moist, cool conditions. Wet conditions can cause soil and plant material to adhere to vehicles, equipment, and footwear. Whenever possible, it is always best to avoid visiting an infested area, especially during the rainy season.

Always know when you are working or recreating in a Phytophthora ramorum-infested area so that proper sanitary measures can be practiced and to assure compliance with state and federal regulations. When in an infested area, especially where conditions are wet, keep vehicles on paved or gravel surfaces if possible. Before leaving the infested area, check yourself, pet(s), vehicle, and equipment to ensure that all mud, soil, organic material, and plant debris (leaves, twigs, etc.) are removed. Lysol, 70% alcohol, or a 10% bleach solution can be used to kill any remaining spores. Keep a cleaning kit (bucket, scrub brush, cleaning solution, & towels) in your vehicle, and use separate tools and footwear in infested areas if possible.


Janice Alexander, UC Cooperative Extension

Dead and dying bark hosts rarely infect other trees. If dead or dying diseased trees are felled for hazard reduction, it is best to leave all material on-site when possible. An excellent way to dispose of larger woody material is to use it as firewood on-site. Smaller material can be chipped and used as mulch on-site, or lopped and scattered close to the ground to reduce fire hazard. While commercial composting of infested material is effective at killing the pathogen, homeowner composting is not recommended.

If infested material must be removed from the site, it should be carefully covered and taken to an approved disposal site within the regulated area, such as an approved landfill, composting facility, or designated collection site for diseased material.


Preventing Disease Transfer between Nurseries

To minimize the risk of infested plant material being transported between nurseries, the following BMPs* should be implemented:

  • Confirm that host stock is propagated from on-site materials, or is received from shipping nurseries under compliance agreements.

* Nursery BMPs developed by the COMTF Nursery Subcommittee- Karen Suslow, Hines Horticulture, and Gail Raabe, San Mateo Co. Agricultural Commissioner, Co-Chairs


Have trained personnelinspect all incoming host plants, regardless of origin, for Phytophthora ramorum symptomsprior to incorporating them into the production facility. Segregate these plants from other host plants, and periodically inspect them for symptoms over the course of a growing season.

  • Off-load incoming shipments to an area that can be cleaned of leafy debris. Sweep debris from the loading pad and truck, and bag it for disposal.
  • Maintain accurate shipping documentation including product, amount, date, and origin to facilitate trace-backs and trace-forwards.

Preventing Infection from Surrounding Woodlands

If a nursery is located in an area where Phytophthora ramorum is found naturally, there are steps that should be taken to minimize the chance of nursery plants becoming infected.

  • Monitor host plants in the surrounding area for disease symptoms, especially in the spring and summer.
  • If practical, remove host plants within 100 feet of the nursery perimeter.
  • Install diversion berms to prevent soil and water movement from surrounding hillsides during storm events.

Place containers/pots on a soil barrier such as gravel, or on raised beds.

  • Monitor irrigation water from sources other than well or municipal water sources to ensure that it is pathogen-free.
  • Overhead irrigation greatly increases the chances of introduction and spread of Phytophthora ramorum, especially in generally infested areas. Use drip irrigation wherever possible. If overhead watering must be used, irrigate in the morning to allow for drying by nightfall.

Preventing Favorable Disease Conditions in the Nursery

Should inoculum or infected plants enter the nursery, it is important to avoid conditions that may foster the pathogen’s survival and spread. The following precautions are recommended to help safeguard nurseries from internal infestations.

  • Shading and overhead irrigation create cool, humid conditions that, while favorable for some nursery crops, are also favorable for the spread and survival of Phytophthora ramorum. Avoid these conditions where possible.
  • Correct low spots or poor drainage that may accumulate water for extended periods. Check and maintain irrigation systems to avoid leaks and uneven watering.

Wounded leaves are the most susceptible to infection. Wherever possible, avoid moving or handling plants during times when environ-mental conditions favor the pathogen.

  • Locate soil and cull piles as far as possible from plants, and cover with clear polyethylene sheets. Dispose of culled plants and plant material as soon as possible.
  • Make sure that all nursery workers are aware of the potential for Phytophthora ramorum infestations, and are familiar with symptoms for early detection.

Preventative Chemical Treatments

Doug Schmidt, UC Berkeley

While there is no known cure for Phytophthora ramorum, there is currently a preventative phosphite fungicide treatment available for use in high-risk landscape settings. In California, risk is largely based on proximity to California bay laurels.

As the treatment is relatively expensive and time consuming, it is not practical for wildland situations.

When treating a tree, the material is injected into the cambium, or sprayed directly on to the lower trunk of bark hosts. Two treatments 6 months apart are required the first year, with yearly treatments thereafter.


Karl Buermeyer,

UC Cooperative Extension

There is currently no eradicative treatment for Phytophthora ramorum on foliar hosts. Research is ongoing to find treatments to prevent foliar hosts, particularly ornamentals, from becoming infected and spreading the disease.


Review Questions

1.What are the two broad categories of measures taken to minimize the spread of Phytophthora ramorum?

1. Regulations and Quarantines

2. Best Management Practices

2. Name 3 levels of commerce that require regulating, and are under different jurisdictions.

1. Within a state (Intrastate)

2. Between states (Interstate)

3. International

3.At what time of year, or under what conditions, are extra precautions necessary when working in Phytophthora ramorum-infested areas?

Under moist conditions or during wet times of the year


Review Questions, continued

4.What should always be done before leaving

an infested area?

Remove host plant material and soil from footwear, vehicles, and equipment

5.What is the best way to dispose of infested plant material?

Burn as firewood on the property, or leave it on site

6.List 4 BMPs to prevent Phytophthora ramorum spread between nurseries.

1. Confirm stock source is not infested

2. Inspect incoming host material for symptoms

3. Clean and dispose of debris from shipping area

4. Keep records of all shipping transactions


Review Questions, continued

7.Name 3 sources of infection for nursery plants in Phytophthora ramorum-infested areas.

1. Infected host plants around the perimeter

2. Soil and water runoff from hillsides

3. Irrigation water from infested water sources

8.What conditions in a nursery may make its environment more susceptible to Phytophthora ramorum infestations?

Shading with overhead irrigation

9.What should be true about a host tree before considering it for preventative phosphite treatment?

It should be a high-value tree, at risk of becoming infected


For additional information on

Phytophthora ramorum and Sudden

Oak Death, please visit the California

Oak Mortality Task Force website: